Surface acoustic wave device method of manufacturing the same, and electronic component using the same

ABSTRACT

A surface acoustic wave (SAW) device includes a piezoelectric substrate, and on this substrate there are provided comb electrodes for forming an inter digital transducer (IDT), reflector electrodes placed closely along a traveling direction of a surface wave generated by the IDT, and a frame-like short-circuited auxiliary electrode having a width varying depending on its portions. This structure allows to uniform electric charges overall the electrode-surfaces, where the electric charges are generated in a heat treatment applied to the piezoelectric substrate during the manufacturing of the SAW device. Thus even after the device is diced into pieces, this structure can prevent damages of the electrodes or degradation in electrical properties due to an electric discharge generated by accumulated electric charges caused by pyroelectricity of the substrate.

TECHNICAL FIELD

The present invention relates to a surface acoustic wave (SAW) device tobe used in communication apparatuses, a method of manufacturing the samedevice, and electronic components using the same device.

BACKGROUND ART

A conventional surface acoustic wave (SAW) device has been manufacturedin the following way: first, form metallic thin film on the overallsurface of a piezoelectric substrate, second, apply resist thereon,expose it to light before development. Then provide it with etching,thereby forming a plurality of desired electrode patterns includingdesired inter-digital transducer (IDT) electrodes, grating reflectorelectrodes (hereinafter referred to as reflector electrodes), dicinglines surrounding the foregoing electrodes, and narrow lines couplingthose elements. Finally, cut the substrate along the dicing lines intopieces of SAW devices.

In the SAW device manufactured by the foregoing method, i.e., apiezoelectric substrate is diced into the pieces, the IDT electrodes andthe reflector electrodes are electrically separated, thus applying heator distortion to the SAW device produces electric charges due topyroelectric effect of the piezoelectric substrate. Uneven amounts ofelectric charges between the respective electrodes cause an electricaldischarge between the IDT electrodes opposite to each other, between thereflector electrodes, or between the IDT electrode and the reflectorelectrode. Those discharges damage the electrodes, or degrade theelectrical properties of the SAW device.

Japanese Patent Application Non-examined Publication No. H11-298289discloses a method for overcoming the problems discussed above.According to this method, short-circuited narrow lines made of metallicthin film are provided inside dicing lines such that the narrow linessurround IDT electrodes and reflector electrodes. Then a plurality ofnarrow lines are provided for connecting electrically thoseshort-circuited narrow lines made of metallic thin film with the IDTelectrodes, thereby electrically uniforming electric charges produced.This structure prevents the SAW device from being damaged and degradedits electrical properties due to electric discharges. In the meantime,dicing lines are border lines that partition plural SAW devices formedon a piezoelectric substrate into pieces. The dicing line is made of thesame material as the IDT electrode, and the material undergoesphoto-lithography and etching before it becomes a dicing line.

In the foregoing structure, i.e., short-circuited narrow lines made ofmetallic thin film are provided inside the dicing lines such that thenarrow lines surround the IDT electrodes and reflectors electrodes, anda plurality of narrow lines are provided for connecting electricallythose short-circuited narrow lines made of metallic thin film with theIDT electrodes, there are still problems as follows: Impedance betweenthe lines becomes higher, so that the electric charges produced cannotbe sufficiently uniformed, which results in discharges between theelectrodes. As a result, the electrodes are damaged or electricalproperties are degraded. Those problems occur in the following cases: acase where a large amount of electric charges is produced due to a sharpchange in temperature, a case of short distances between electrodes, acase where the coupled electrodes are away from each other, a case wherethe width of the line coupling the short-circuited line made of metallicthin film with the IDT electrode is narrow, a case where the widths oflines used for coupling are narrower than a meander line, or some partsof the line are narrower than the other parts of the line.

SUMMARY OF THE INVENTION

The present invention solves the foregoing problems and aims to providea SAW device, a method of manufacturing the same device, and electroniccomponents using the same device. When the SAW device of the presentinvention is manufactured, electric charges produced by a heat treatmentapplied to a piezoelectric substrate are uniformly spread overrespective electrode-surfaces of the SAW device. Thus after thesubstrate is split into pieces of SAW devices, damages of the electrodesby an electric discharge or degradation of electrical propertiesaccompanying the electric potential differences due to pyroelectricityof the substrate can be prevented.

In order to solve the foregoing problems, the SAW device of the presentinvention comprises the following elements:

-   -   a piezoelectric substrate;    -   comb electrodes forming an IDT;    -   reflector electrodes to be disposed closely along a traveling        direction of a surface wave generated from the IDT; and    -   a frame-like short-circuited auxiliary electrode having        different widths depending on its portions and to be disposed        surrounding the comb electrodes and the reflector electrodes.

A method of manufacturing the SAW device of the present inventioncomprises the following steps:

-   -   depositing metal to form metallic thin film on the piezoelectric        substrate;    -   providing a plurality of sets of the following electrodes:        -   comb electrodes formed by etching the metallic thin film,            the comb electrodes forming the IDT;        -   reflector electrodes formed closely along a traveling            direction of surface waves generated by the IDT;        -   frame-like short-circuited auxiliary electrodes disposed at            least around the comb electrodes and the reflector            electrodes, and having widths varying depending on their            portions, and    -   cutting the substrate between short-circuited auxiliary        electrodes adjacent to each other.

An electronic component of the present invention comprises the followingelements:

-   -   a base substrate including a leader electrode on a box-shaped        bottom and a terminal electrode conductive to the leader        electrode;    -   a lid covering the base substrate for sealing the inside of the        base substrate;    -   a SAW device disposed on a bottom of the base substrate; and    -   a coupling member for electrically coupling the SAW device with        the leader electrode of the base substrate.

The electronic component is characterized by a use of the SAW devicehaving the structure discussed previously.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a plan view showing a structure of electrode patterns of aSAW device in accordance with a first exemplary embodiment of thepresent invention, and FIG. 1B is a plan view showing a plurality of theSAW devices formed on a piezoelectric substrate.

FIG. 2 is a sectional view of an electronic component using the SAWdevice shown in FIG. 1.

FIG. 3 is a plan view showing a structure of electrode patterns of a SAWdevice in accordance with a second exemplary embodiment of the presentinvention.

FIG. 4 is a plan view showing a structure of electrode patterns of a SAWdevice in accordance with a third exemplary embodiment of the presentinvention.

FIG. 5A is a plan view showing a structure of electrode patterns of aSAW device in accordance with a fourth exemplary embodiment of thepresent invention, and FIG. 5B is a plan view showing a plurality of theSAW devices formed on a piezoelectric substrate.

FIG. 6 is a plan view showing a structure of electrode patterns of a SAWdevice in accordance with a fifth exemplary embodiment of the presentinvention.

FIG. 7 is a plan view showing a structure of electrode patterns of a SAWdevice in accordance with a sixth exemplary embodiment of the presentinvention.

FIG. 8 is a plan view showing a structure of electrode patterns of a SAWdevice in accordance with a seventh exemplary embodiment of the presentinvention.

FIG. 9 is a plan view showing a structure of electrode patterns of a SAWdevice in accordance with an eight exemplary embodiment of the presentinvention.

PREFERRED EMBODIMENTS OF THE INVENTION

Exemplary embodiments of the present invention are demonstratedhereinafter with reference to the accompanying drawings.

Exemplary Embodiment 1

FIG. 1A is a plan view showing a structure of electrode patterns of asurface acoustic wave (SAW) device in accordance with the firstexemplary embodiment of the present invention, and FIG. 1B is a planview showing a plurality of the SAW devices, one of which is shown inFIG. 1A, formed on a substrate. FIG. 2 is a sectional view of anelectronic component in which the SAW device sealed by a packagecomprising a base substrate and a lid.

SAW device 10 of the present invention has the following structure:

-   -   On piezoelectric substrate 1, the electrodes below are disposed:        -   comb electrodes 2 forming an IDT;        -   reflector electrodes 3 disposed at the vicinity of the            traveling direction of surface acoustic wave excited by comb            electrodes 2, reflector electrodes 3 being placed at a given            distance from comb electrodes 2;        -   input/output leader electrodes 4 a, 5 a, input/output            terminal electrodes 4 b, 5 b and belt-like connecting            electrode 18, each led out from comb electrodes 2; and        -   frame-like short-circuited auxiliary electrode 6 surrounding            the foregoing electrodes and having different width            depending on its portions. Outside frame-like            short-circuited auxiliary electrode 6, clearance 8 remains            partially due to dicing, and the surface of substrate 1 is            exposed in clearance 8. At given places of electrode 6 and            input/output terminal electrodes 4 b, 5 b, bumps 7 are            formed. Bumps 7 couple leader electrode 13 of base substrate            9 with terminal electrodes, 4 b, 5 b and auxiliary electrode            6.

As shown in FIG. 2, base substrate 9 is shaped like a box at which baseleader electrode 13 is disposed, and leader electrode 13 is conductivewith outer terminal electrode 14. Bumps 7 placed at given places of SAWdevice 10 not only electrically connects to leader electrode 13 but alsomechanically fixes leader electrode 13. Bonding member 16 such as Au—Snsolder is provided to lid 15. Bonding member 16 seals the inside of basesubstrate 9, thereby forming an electronic component.

FIG. 1 and FIG. 2 are schematic drawings illustrating structures inaccordance with the first embodiment, and those drawings do not indicatedimensional relations of respective elements. The drawings of the SAWdevice hereinafter used also do not indicate dimensional relations.

Some piezoelectric substance produces electric potential due topyroelectricity or piezoelectricity. Differences of electric potentialin places produce electric potential differences. If the electricpotential difference exceeds a certain value, an electric dischargeoccurs, which sometime damages elements or degrades electricalproperties. One of effective preventive measures against this problem isto lower the electric potential due to pyroelectricity orpiezoelectricity, or to restore electric potential differences to a flatpotential as quick as possible.

The present invention is based on the finding that reserving areas oflow impedance as large as possible in the electrode pattern of SAWdevice 10 is an effective method for reducing electric potentialdifferences as quick as possible. To be more specific, in the electrodepatterns of SAW device 10 of the present invention, there are placedcomb electrodes 2 forming an IDT, and reflector electrodes 3 disposed onboth sides of comb electrodes 2 and closely along the travelingdirection of the surface wave generated by comb electrodes 2, onpiezoelectric substrate 1. Frame-like short-circuited auxiliaryelectrode 6 surrounds comb electrodes 2 and reflector electrodes 3.Short-circuited auxiliary electrode 6 is coupled with leader electrode13 of base substrate 9 to which SAW device 10 is mounted. Leaderelectrode 13 is conductive with terminal electrode 14 and works as agrounding electrode. Short-circuited auxiliary electrode 6, as shown inFIG. 1A, is shaped like a frame uniformly formed, i.e., the frame isapprox. symmetric with respect to the center of the IDT, on the surfaceof device 10 where electrodes are formed.

Further, belt-like input/output leader electrodes 4 a and 5 a, bothcoupled with each one of comb electrodes 2, face each other and haveapprox. the same areas. In addition to this, input/output terminalelectrodes 4 b and 5 b coupled with input/output leader electrodes 4 aand 5 a also face each other and have approx. the same areas. Reflectorelectrodes 3 and short-circuited auxiliary electrode 6 are openelectrically. The electrodes have the foregoing structure.

As discussed above, in SAW device 10, belt-like input/output leaderelectrodes 4 a, 5 a, and input/output terminal electrodes 4 b, 5 b haveapprox. the same areas. Further, short-circuited auxiliary electrode 6is shaped like a frame substantially symmetric with respect to thecenter of the IDT. This structure can eliminate local areas where largeamounts of electric charges due to pyroelectricity of the substrate areaccumulated. Thus the electric potential differences between thepatterns of respective electrodes can be substantially reduced.Therefore, even reflector electrodes 3 and comb electrodes 2 areelectrically open with respect to short-circuited auxiliary electrode 6,electric charges produced at electrodes 2 and 3 can be uniformed, andthus no electric potential difference occurs between them, wherebyoccurrence of an electric discharge can be prevented. As a result, theelectrodes of the SAW device can be prevented, and the degradation ofelectrical properties can be also prevented. In order to uniform theelectric potentials due to the pyroelectricity for reducing the electricpotential differences between the electrode patterns, it is effective towiden, as much as possible within the design allowance, electrode 6 tominimize impedance. It is also effective to place electrode 6 as closeas possible to comb electrodes 2 and reflector electrodes 3. For thispurpose, it is necessary to employ the max. width within the designallowance in short-circuited auxiliary electrode 6, thus the width ofelectrode 6 varies depending on places as shown in FIG. 1B.

Short-circuited auxiliary electrode 6, having width of as wide aspossible, surrounds comb electrodes 2 and reflector electrodes 3,thereby reducing impedance, so that electric potential differencesproduced by accumulated electric charges due to pyroelectricity ofsubstrate 1 can be quickly uniformed. This uniformity of the electricpotential differences produces greater effect as an area of theelectrodes increase, where the electrodes, including electrode 6,commonly connected in SAW device 10. Thus short-circuited auxiliaryelectrode 6 is desirably formed by lines having a width as wide aspossible rather than by narrow lines.

In this first embodiment, short-circuited auxiliary electrode 6 iscoupled with a grounding electrode of terminal electrodes 14 provided tobase substrate 9, so that electric charges produced in substrate 1 canescape from electrode 6 to the outside via terminal electrode 14. Thusthe influence of the electric charges due to pyroelectricity can besubstantially reduced with respect to SAW device 10.

When SAW device 10 is heated, electric charges are produced because ofpyroelectricity, and those electric charges occur from piezoelectricsubstrate 1 that has pyroelectricity. Device 10 is heated uniformlyoverall in the regular manufacturing process, therefore electric chargesoccur from overall device 10. However, in SAW device 10, there are aplurality of independent electrode patterns, and input/output terminalelectrodes 4 b, 5 b have the largest areas in general. Thus the largestelectric potential difference tends to occur in these electrodes. Inorder to uniform the electric charges occur in substrate 1 overall andreduce the electric potential differences, short-circuited auxiliaryelectrode 6 having the following features is provided: (a) surroundingcomb electrodes 2 and reflector electrodes 3; (b) symmetric with respectto input/output terminal electrodes 4 b, 5 b ; and (c) belt-like shapewith a width as wide as possible. This structure can suppress theelectric discharge.

There is another method of preventing the SAW device from being damagedby the discharge due to accumulation of electric charges. For instance,between adjacent electrodes, a narrowed clearance is reserved inadvance, and when an accumulation of electric charges reaches to acertain level, discharge them locally within a range of not damaging theSAW device. This method, however, is not preferable because it producesnoises during an operation of the device. Accordingly, in order toprevent the SAW device from being damaged due to accumulation ofelectric charges, it is effective to provide frame-like short-circuitedauxiliary electrode 6 close to comb electrodes 2 and reflectorelectrodes 3. The width of electrode 6 is preferably as wide aspossible.

Further, input/output leader electrodes 4 a, 5 a and input/outputterminal electrodes 4 b, 5 b are placed opposite to each other, andrespective areas are approx. equal to each other. In addition to thosestructural preparations, frame-like short-circuited auxiliary electrode6 is placed uniformly overall, i.e., the frame is substantiallysymmetric with respect to the center of the IDT. The foregoing structureeliminates regions where electric charges accumulate locally, and thusthe electric potential differences can be uniformed.

In this embodiment, a pair of comb electrodes 2 and a pair of reflectorelectrodes 3 are prepared; however, the present invention is not limitedto this preparation, and a SAW device with more multi-steps producessimilar advantages to those discussed above.

Next, a method of manufacturing SAW device 10 of the present inventionis demonstrated hereinafter. Form laminated metallic thin film onpiezoelectric substrate 1 by, e.g., sputtering. A single-crystalsubstrate made of, e.g., LiTaO₃ or LiNbO₃ is used as substrate 1. Themetallic thin film is formed of titan (Ti) film as the lowest layer,alloy film of Al—Sc—Cu (Aluminum-Scandium-Copper) as the middle layer,Ti film as the upper layer, and aluminum film evaporated on top of theupper layer. Next, apply photo-resist onto the foregoing metallic thinfilm, and undergo the film in photo-lithography process and etchingprocess, thereby working the metallic thin film into desiredelectrode-patterns. After those steps, photo-lithography and etchingprocesses are further applied so that the Al film, i.e., the upper mostlayer on comb electrodes 2, can be removed. As a result, soft metallicfilm, i.e., Al film formed by evaporation remains on input/output leaderelectrodes 4 a, 5 a, input/output terminal electrodes 4 b, 5 b, andshort-circuited auxiliary electrode 6. This removal of Al film can bedone by, e.g., wet-etching. In this case, the Al film can be removedwith ease utilizing a selection ratio of etching Al vs. Ti. FIG. 1Bshows the electrode-patterns thus formed.

Then cut respective clearances 8 of short-circuited auxiliary electrode6 between adjacent SAW devices 10 with a dicing device, so that SAWdevices 10 in a predetermined shape are obtained. In this embodiment,instead of cutting along dicing lines conventionally provided, cut thecenter of clearance 8 of electrode 6, so that the dicing lines becomeeventually not necessary, which can simplify the design of SAW device 10and further downsize the SAW device.

The metallic thin film is not limited to the materials and the structurediscussed above. Films of Al, Ti, Cu, Cr, Ni or an alloy of those metalscan be laminated on top of the foregoing metallic thin film, or athree-layer structure formed of Al film as the lowest layer, Al—Cu alloyfilm as the middle layer and Ti film as the upper layer can be used. Assuch, various materials and structures are applicable, and any number oflayers more than one can be laminated, and an order of layers is notlimited to the foregoing orders. This kind of laminated electrode-filmcan increase withstand electric power and prevent the electrodes frombeing damaged by an electric discharge.

On top of the metallic thin film discussed above except at least combelectrodes 2, film of soft material such as aluminum can be evaporatedby the following methods: In the case where the surface layer of theelectrode film is made of Ti film, wet-etching can selectively removethe Ti film. In the case where the surface layer is made of Al film,photo-resist is formed in advance, then Al film is evaporated, i.e., alift-off method can do it with ease.

Next, the steps of mounting SAW devices 10 thus obtained onto basesubstrate 9 are demonstrated hereinafter with reference to FIG. 2. Afterregistration of leader electrodes 13 provided on the bottom ofbox-shaped base substrate 9 with bumps 7 formed on SAW devices 10, theyare electrically coupled and devices 10 are mechanically fixed. Thereare several methods for this bump-coupling such as: coupling withconductive resin, coupling with soldered bumps, ultrasonic Au—Aucoupling (the surface of the leader electrode and bumps 7 are formed ofgold), eutectic Au—Sn coupling (Sn film is formed on the surface ofleader electrode and bumps 7 are made of gold). Bumps 7 can be formed byplating or wire-bonding.

SAW devices 10 are thus fixed onto base substrate 9, then bring lid 15into contact with base substrate 9 and heat it to fix to substrate 9,thereby forming a sealed electronic component. Lid 15 has a bondingmember made of such as Au—Sn solder.

The bump-bonding method discussed above allows larger contact areasbetween leader electrodes 13 and bumps 7, so that bonding reliabilitycan be increased. On the other hand, if the heating at the bump bondingproduces thermal strain, electrode-film sometimes peals off and thebonding reliability decreases. The present invention is based on thefinding that when at least the upper most layer of the electrode-film isformed by evaporation, the thermal strain at the bump bonding can bemoderated, which prevents the electrode-film from peeling off. Further,the film made by evaporation has another advantage that it suppresseselectrochemical corrosion to the electrode-film during the step ofcutting or washing.

Because the evaporated film tends to form thin film having the sameorientation as the material, so that the bonding between metal grains issupposed to be strengthened. Therefore, at least the upper most layerthat contacts with the bumps is formed by evaporation, then theelectrode-film can not be peeled off by distortion due to the bonding,and the electrochemical corrosion can be also suppressed.

Metallic thin film to be formed by evaporation is preferably made ofsoft material because of better bonding with bumps. As the softmaterial, aluminum, Au, Al—Cu alloy made from aluminum plus at least oneof Cu, Sc, Cr, Ni, or Ti can be used.

On top of the upper most layer that contacts with bumps, another layercan be formed by evaporation. This structure can also produce a similaradvantage.

The location where bumps are formed is, of course, not limited to thelocations shown in FIG. 1A. Further, belt-like input/output leaderelectrodes 4 a, 5 a and input/output terminal electrodes 4 b, 5 b areelectrically independent of each other. Therefore, electrical propertiesof respective devices 10 can be measured by applying probes to theirinput/output terminal electrodes 4 b, 5 b with given electrode patternskept formed on substrate 1 as shown in FIG. 1B. Accordingly, screeningon properties can be done before elastic surface devices 10 are cut intopieces, and conforming pieces only can be collected to assembleelectronic components after the cutting.

As discussed above, according to the present invention, surround combelectrodes 2 and reflector electrodes 3 with frame-like short-circuitedauxiliary electrode 6 of which width varies depending on places, andform at least the upper most layer that contacts with bumps 7 byevaporation. This structure can reduce the electric potentialdifferences produced by pyroelectricity of piezoelectric substrate 1.Further, this structure can prevent peeling off of the electrode-film atbonded sections, and suppress electrochemical corrosion. Laminatedelectrode-film increase withstand electric power, so that whenaccumulated electric charges develop an electric discharge, theelectrode-film is hardly to be damaged, which further strengthens thewithstand electric discharge.

In manufacturing electronic components to which SAW devices 10 aremounted, not only the bump-bonding method discussed above but also,e.g., a wire-bonding method can be used for bonding.

Exemplary Embodiment 2

The second exemplary embodiment of the present invention is demonstratedhereinafter with reference to FIG. 3. In FIG. 3, the same elements asthose in FIG. 1A have the same reference marks.

A pair of structures are prepared, each one of them has three combelectrodes 201, 202, 203, and reflector electrodes 3 disposed on bothsides of the three comb electrodes. At each one of center combelectrodes 202 placed between electrodes 201 and 202, input/outputleader electrodes 4 a, 5 a, input/output terminal electrodes 4 b, 5 b,grounding leader electrode 21 a, and grounding terminal electrode 21 bare disposed as shown in FIG. 3. Frame-like short-circuited auxiliaryelectrode 6 is formed such that electrode 6 surrounds the configurationdiscussed above. Reflector electrodes 3 on both the sides areelectrically coupled with each other via first connecting electrode 17,and comb electrodes 201, 203 on both sides are electrically coupled witheach other via second connecting electrode 20 with respect toshort-circuited auxiliary electrode 6. Outside electrode 6, thereremains clearance 8 after dicing. The surface of substrate 1 is exposedfrom clearance 8. The other ends of comb electrodes 201, 203 are coupledwith each other via belt-like electrode 18. Bumps 7 are prepared oninput/output electrodes 4 b, 5 b and auxiliary electrode 6 at givenplaces. SAW device 100 is thus constructed. A manufacturing method of anelectronic component using this SAW device 100 is similar to thatdemonstrated in the first embodiment, the description thereof is thusomitted here.

In the foregoing structure, reflector electrode 3 and comb electrodes201, 203 on both sides are coupled with short-circuited auxiliaryelectrode 6 via belt-like first connecting electrode 17 and the secondconnecting electrode. Thus wide areas of SAW device 100 are commonlyconnected and have an identical electric potential. As a result, ifdevice 100 undergoes temperature changes and electric potentials occurdue to pyroelectricity of substrate 1, this structure including an openelectrode-pattern allows to substantially reduce electric potentialdifferences.

An effect of the electrical coupling of comb electrodes 201, 203,reflector electrodes 3 with short-circuited auxiliary electrode 6depends on a design of the electrode-patterns; however, the design isonly required to lower an impedance in order to uniform electricpotentials, and there is no limitation about a width of electrodes or anumber of electrodes. It is preferable, however, to have a width of aswide as possible and electrodes as many as possible, for producing moreeffective result.

In this embodiment, since the electrodes including comb electrodes 201,203 and reflector electrodes 3 are commonly coupled, respective sectionseventually have an identical electric potential even if differentelectric potentials occur at the respective sections. As a result,excellent SAW device 100, free from damages of the electrodes ordegradation in properties due to an electric discharge, can bemanufactured with ease.

Exemplary Embodiment 3

The third exemplary embodiment of the present invention is demonstratedhereinafter with reference to FIG. 4. In FIG. 4, the same elements asthose in FIG. 1A have the same reference marks.

In this embodiment, reflector electrode 19 is formed of meander lines,and both the ends of electrode 19 are electrically coupled with combelectrodes 2 as shown in FIG. 4. In other words, except the electriccoupling of reflector electrode 19 formed of meander lines with combelectrodes 2, the structure of the third embodiment is the same as thatused in the first embodiment. Further, a method of manufacturing anelectronic component using SAW device 110 and base substrate 9, lid 15shown in FIG. 2 is similar to that demonstrated in the first embodiment.

In FIG. 4, reflector electrode 19 formed of meander lines iselectrically coupled with comb electrodes 2, and they become conductivewhen a dc signal is used or in a low frequency region. However, in ahigh frequency region where SAW device 110 usually works, the impedancein the meander lines increases, so that electrodes 19 and 2 actuallybecome open. On the other hand, since reflector electrode 19 formed ofmeander lines is electrically coupled with comb electrodes 2, electriccharges developed due to pyroelectricity of piezoelectric substrate 1can be uniformed in wider areas of the electrodes. As a result, electricpotential differences can be reduced.

In other words, the electric coupling of reflector electrode 19 formedof meander lines with comb electrodes 2 allows these two types ofelectrodes to be actually open in a high frequency region, i.e., anactual working condition, and no inconvenience occurs in operation ofSAW device 110. As for the electric potential due to pyroelectricity,electric conductivity between comb electrodes 2 and reflector electrode19 allows to reduce the electric potential differences.

Further, belt-like input/output leader electrodes 4 a, 5 a coupled withcomb electrodes 2 are disposed opposite to each other, and electrodes 4a, 5 a have an approx. equal area. Input/output terminal electrodes 4 b,5 b coupled with electrodes 4 a, 5 a are also disposed opposite to eachother, and they have approx. an equal area. This structure substantiallyeliminates electric potential differences even if the respectiveelectrode patterns have electric potentials due to pyroelectricity. As aresult, excellent SAW device 110, free from damages of the electrodes ordegradation in properties due to an electric discharge, can bemanufactured with ease.

Exemplary Embodiment 4

The fourth exemplary embodiment of the present invention is demonstratedhereinafter with reference to FIGS. 5A and 5B. FIG. 5A is a plan viewshowing a structure of an electrode pattern, and FIG. 5B is a plan viewshowing a plurality of the SAW devices formed on a piezoelectricsubstrate. In FIGS. 5A and 5B, the same elements as those in FIG. 1Ahave the same reference marks. SAW device 120 in accordance with thisfourth embodiment differs from SAW device 10 of the first embodimentonly in forming dicing lines 80 made of the same material as theelectrodes at outer periphery of device 10. In other words, when thesubstrate is cut along dicing lines into pieces, the dicing linesdisappear; however, dicing lines 80 of the fourth embodiment have awidth wide enough to positively remain at the outer periphery after thedicing.

In this embodiment, dicing lines 80 electrically shorted with SAW device120 are disposed on substrate 1 together with device 120. This structureallows to uniform electric potential differences between the respectiveelectrode patterns if a large electric potential due to pyroelectricitywhich is activated by a large temperature change to the substrate beforethe dicing. After substrate 1 is diced into pieces, parts of dicinglines 80 remain keeping a frame-like shape at the outer periphery of SAWdevice 120, so that the electric potential differences are furtherreduced. A dicing device cuts substrate 1 along on dicing lines 80, sothat registration accompanying the cutting can be done with ease.

If plural sets of comb electrodes 2 and reflector electrodes 3 aredisposed on a SAW device, the device can obtain similar advantages tothose discussed above. A manufacturing method of SAW device 120 inaccordance with the fourth embodiment is similar to the method ofmanufacturing device 10 in accordance with the first embodiment exceptthe dicing of substrate 1 along on dicing lines 80.

Exemplary Embodiment 5

The fifth exemplary embodiment of the present invention is demonstratedhereinafter with reference to FIG. 6. In FIG. 6, the same elements asthose in FIG. 3 have the same reference marks. SAW device 130 inaccordance with this fifth embodiment differs from SAW device 100 of thesecond embodiment only in forming dicing lines 80 made of the samematerial as the electrodes at outer periphery of device 100. Shape,structure and method of manufacturing are the same, except the itemdiscussed above, as those in the second embodiment. Dicing lines 80 ofthe fifth embodiment have a width wide enough to positively remain atthe outer periphery after the dicing.

Second connecting electrode 20, which electrically couples combelectrodes 201, 203 with short-circuited auxiliary electrode 6, ispreferably tapered at its pattern width toward, e.g., electrode 6,because it is not desirable to have a high impedance section at somemidpoints of its pattern. The width of second connecting electrode 20 ispreferably wider than that of dicing line 80.

Dicing lines 80 are provided as discussed above, and they remain keepinga frame-like shape after the cutting, so that devices 130 on substrate 1can be kept stable against temperature changes during working steps.When devices 130 as the pieces are mounted to a base substrate, atemperature changes; however they are free from damages or degradationin properties due to an electric discharge. Electronic components usingthis excellent SAW device can be manufactured with ease.

Exemplary Embodiment 6

The sixth exemplary embodiment of the present invention is demonstratedhereinafter with reference to FIG. 7, which is a plan view showing astructure of electrode-patterns of SAW device 140 in accordance with thesixth embodiment. In FIG. 7, the same elements as those in FIG. 6 havethe same reference marks. As shown in FIG. 7, SAW device 140 inaccordance with the sixth embodiment has third connecting electrodes 22,which electrically couple dicing lines 80 with short-circuited auxiliaryelectrode 6 in device 130 of the previous fifth embodiment. A method ofmanufacturing electronic components using this SAW device 140 is similarto that demonstrated in the first embodiment, and the construction ofthe electronic components is also similar to that of the firstembodiment. In this sixth embodiment, the width of dicing lines 80 iswide enough to positively remain at the outer periphery after thedicing.

As discussed above, short-circuited auxiliary electrode 6 iselectrically coupled with dicing lines 80 via third connectingelectrodes 22, so that electric potentials become uniform throughout theelectrodes including comb electrodes 201, 203 on both sides, reflectorelectrodes 3, electrode 6 and dicing lines 80 even if electric chargesoccur in piezoelectric substrate 1, because they are commonly coupledelectrically. This structure further effectively prevents an electricdischarge due to an electric potential difference from occurring.

The electrode patterns electrically connecting dicing lines 80,short-circuited auxiliary electrode 6, comb electrodes 201, 203 on bothsides and reflector electrodes 3 can be line-shaped or belt-like as longas they have a low impedance. There is no limit to a number of electrodepatterns.

Exemplary Embodiment 7

The seventh exemplary embodiment of the present invention isdemonstrated hereinafter with reference to FIG. 8. In FIG. 8, the sameelements as those in FIG. 6 have the same reference marks. As shown inFIG. 8, SAW device 150 in accordance with the seventh embodiment differsfrom device 140 of the sixth embodiment only in reflector electrodes 3left open from the short-circuited auxiliary electrode. Other respectsand the method of manufacturing are similar to those of SAW device 140.

Since comb electrodes 201, 203 on both sides, short-circuited auxiliaryelectrode 6 and dicing lines 80 are commonly connected electrically,when electric charges occur in piezoelectric substrate 1, this structureallows to reduce electric potential differences between those elementsalthough comb electrode 202 and reflector electrodes 3 are electricallyopen. As a result, this structure can reduce electric potentialdifferences and suppress an electric discharge, so that a reliable SAWdevice is obtainable and an electronic component using this device canbe realized.

Exemplary Embodiment 8

The eighth exemplary embodiment of the present invention is demonstratedhereinafter with reference to FIG. 9, which is a plan view illustratinga structure of electrode-patterns of SAW device 160 in accordance withthe eight embodiment. In FIG. 9, the same elements as those in FIG. 4have the same reference marks. SAW device 160 in accordance with thiseighth embodiment differs from SAW device 110 of the third embodimentonly in forming dicing lines 80 at the outer periphery of device 110.Other respects and the method of manufacturing are similar to those inthe third embodiment except the item discussed above. Dicing lines 80 ofthe eighth embodiment have a width wide enough to positively remain atthe outer periphery after the dicing.

Similar to the description about SAW device 110 in the third embodiment,in this SAW device 160, reflector electrodes 19 formed of meander linesis electrically coupled with comb electrodes 2. When a dc signal is usedor in a low frequency range, reflector electrodes 19 and comb electrodes2 are conductive. However, in a high frequency region where SAW device160 usually works, the impedance in the meander lines increases, so thatelectrodes 19 and 2 actually become open, which does not influence tothe electric properties of device 160. This is similar to device 110demonstrated in the third embodiment.

In SAW device 160 of this embodiment, reflector electrode 19 formed ofmeander lines is electrically coupled with comb electrodes 2, andframe-like dicing lines 80 similar to frame-like short-circuitedauxiliary electrode 6 are provided. Therefore, electric chargesgenerated by pyroelectricity of piezoelectric substrate 1 are uniformedat the respective electrode-patterns, thereby further reducing theelectric potential differences at respective parts.

In this embodiment, dicing lines 80 and short-circuited auxiliaryelectrode 6 are electrically open; however, the present invention is notlimited to this structure, and electrode 6 is electrically coupled withdicing lines 80 via one or more than one connecting electrode.

In embodiment 1 through embodiment 8, a pair of a comb electrode and areflector electrode or two pairs of them are prepared; however, thepresent invention is not limited to this structure, and more numbers ofmulti-step structure can produce similar advantages to those discussedabove.

INDUSTRIAL APPLICABILITY

According to the present invention, a frame-like short-circuitedauxiliary electrode, of which width varies depending on places,surrounds comb electrodes and a reflector electrode. This structureallows to reduce electric potential differences betweenelectrode-patterns when electric charges occur due to thepyroelectricity of the substrate, which is activated by a temperaturechange, not only in working steps on a substrate-by-substrate basis butalso after the dicing, i.e., in working steps on a piece-by-piece basis.As a result, an electric discharge can be prevented, and a SAW devicefree from damages or degradation in properties is obtainable, further,an electronic component using this device can be manufactured with ease.

1. A surface acoustic wave (SAW) device comprising: a piezoelectricsubstrate; a comb electrode formed on said substrate; a reflectorelectrode disposed adjacent said comb electrode; and a frame-likeshort-circuited auxiliary electrode, of which width varies depending onplaces, for surrounding said comb electrode and said reflectorelectrode, wherein a part of said comb electrode is electrically coupledwith said auxiliary electrode.
 2. The SAW device of claim 1, furthercomprising a dicing line at outer periphery of said auxiliary electrode,wherein an input/output leader electrode to be coupled with said combelectrode and an input/output terminal electrode to be coupled with theleader electrode are disposed at an inner periphery of said frame-likeauxiliary electrode, and a part of said comb electrode is electricallycoupled with said auxiliary electrode.
 3. The SAW device of claim 1,wherein at least three pairs of said comb electrodes are disposed atgiven places, and said comb electrodes on both sides of the plurality ofsaid electrodes are coupled with each other and also electricallycoupled with said auxiliary electrode.
 4. The SAW device of claim 2,wherein at least three pairs of said comb electrodes are disposed atgiven places, and said comb electrodes on both sides of the plurality ofsaid electrodes are coupled with each other and also electricallycoupled with said auxiliary electrode.
 5. The SAW device of claim 1,wherein said comb electrode is electrically coupled with said auxiliaryelectrode via at least a single second connecting electrode which isshaped like one of a line and a belt.
 6. The SAW device of claim 2,wherein said comb electrode is electrically coupled with said auxiliaryelectrode via at least a single second connecting electrode which isshaped like one of a line and a belt.
 7. A surface acoustic wave (SAW)device comprising: a piezoelectric substrate; a comb electrode formed onsaid substrate; a reflector electrode disposed adjacent said combelectrode; a frame-like short-circuited auxiliary electrode, of whichwidth varies depending on places, for surrounding said comb electrodeand said reflector electrode; and a dicing line at outer periphery ofsaid auxiliary electrode, wherein said dicing line is electricallycoupled with said auxiliary electrode.
 8. The SAW device of claim 7,wherein said dicing line is electrically coupled with said auxiliaryelectrode via at least a single third connecting electrode which isshaped like one of a line and a belt.
 9. The SAW device of claim 8,wherein the third connecting electrode has a width at least wider thanthat of said dicing line.
 10. A surface acoustic wave (SAW) devicecomprising: a piezoelectric substrate; a comb electrode formed on saidsubstrate; a reflector electrode disposed adjacent said comb electrode;and a frame-like short-circuited auxiliary electrode, of which widthvaries depending on places, for surrounding said comb electrode and saidreflector electrode, wherein said reflector electrode is formed of ameander line, and both ends of said reflector electrode are electricallycoupled with said comb electrodes respectively.
 11. The SAW device ofclaim 1, further comprising a bump formed on at least one of said combelectrode, said reflector electrode and said auxiliary electrode.